The long-term goal of this project is to trace the developmental course of shared attention between young children and their social partners. Our central argument is that the scope and organization of shared attention is transformed repeatedly as children acquire new ways to coordinate actions and represent events Our current longitudinal research examines the transformation of joint attention that occurs as typically developing toddlers become increasingly competent symbol users, and it documents how this process is impacted by autism, a developmental disorder characterized by joint attention deficits. In this continuation application, we pursue three aims: to relate variations in the trajectory of joint attention development to individual differences in typically developing children's propensities to engage with people and with objects; to describe further atypical patterns of joint attention development that may reflect extreme variations in object and social orientation and in language acquisition; and to continue to trace joint attention development after infancy into the preschool years as new representational skills are mastered. We continue to observe 48 typically developing children and 24 children with autism who are currently enrolled in the project, and we recruit 48 new participants, half of whom have Down syndrome and half who are late talkers. Each child and mother is videotaped 8 times in a Communication Play. The first five visits occur during a one year interval so that we can trace the emergence of symbol-infused joint attention during interactions that focus on requesting, social interacting, shared referring, and discussing past and future. The last three visits occur at age 3-1/2, 4-1/2 and 5-1/2 and probe the emergence of language mediated joint attention during interactions that focus on internal states, narrating the past and future, and graphic symbols. The rate of language acquisition and interests in objects and social domains are also assessed. Videotapes will be transcribed and coded to document the child's attention to people, objects, and symbols; the child's symbolic actions; and the mother's attention-directing actions toward symbols. Growth curves will be examined to chart the course of joint attention as a function of language onset and child orientation to people and to objects. This systematic longitudinal study of developmental changes in shared attention will provide a fuller view of how children are introduced to symbols as they communicate with their caregivers and how symbols expand the scope and affect the organization of shared attention. This view should further the formulation of models of representational development from infancy through early childhood as well as inform understandings of developmental disorders such as autism, Down syndrome, and late speech onset.